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| United States Patent |
6,133,906
|
|
Geaghan
|
October 17, 2000
|
Display-integrated stylus detection system
Abstract
A system and method of measuring the position of a stylus relative to a
computer information display device. The position is used to generate
coordinates for the purpose of interacting with the computer. Applications
may include pointing to icons on the display, picking menu items, editing
of computer generated images, and feedback for input of hand drawn
characters and graphics. The system uses the electrodes of the display
device as part of the positioning circuit.
| Inventors:
|
Geaghan; Bernard O. (Andover, MA)
|
| Assignee:
|
MicroTouch Systems, Inc. (Methuen, MA)
|
| Appl. No.:
|
434558 |
| Filed:
|
May 4, 1995 |
| Current U.S. Class: |
345/179; 178/18.01 |
| Intern'l Class: |
G09G 005/00 |
| Field of Search: |
178/18-20
345/173,174
341/33,32
|
References Cited
U.S. Patent Documents
| 3761877 | Sep., 1973 | Fernald | 178/18.
|
| 3772685 | Nov., 1973 | Masi | 341/31.
|
| 3832693 | Aug., 1974 | Ishizaki et al. | 345/173.
|
| 3990070 | Nov., 1976 | Spence | 341/26.
|
| 4058849 | Nov., 1977 | Fitzgerald et al. | 364/52.
|
| 4125873 | Nov., 1978 | Chesarek | 345/202.
|
| 4190833 | Feb., 1980 | Bejting et al. | 345/80.
|
| 4345248 | Aug., 1982 | Togashi et al. | 345/90.
|
| 4363029 | Dec., 1982 | Piliavin et al. | D10/39.
|
| 4405921 | Sep., 1983 | Mukaiyama | 345/182.
|
| 4525032 | Jun., 1985 | Hilsum | 349/12.
|
| 4639720 | Jan., 1987 | Rympalski et al. | 340/712.
|
| 4785564 | Nov., 1988 | Gurtler | 345/168.
|
| 4839634 | Jun., 1989 | More et al. | 178/18.
|
| 4841290 | Jun., 1989 | Nakano et al. | 345/179.
|
| 4893115 | Jan., 1990 | Blanchard | 345/174.
|
| 4917308 | Apr., 1990 | Meadows | 239/590.
|
| 5162782 | Nov., 1992 | Yoshioka | 345/173.
|
| 5194862 | Mar., 1993 | Edwards | 341/33.
|
| 5283556 | Feb., 1994 | Ise | 345/174.
|
| Foreign Patent Documents |
| 2161935 | Jan., 1986 | GB.
| |
| 2223986 | Jul., 1988 | GB.
| |
| 2250822 | Aug., 1993 | GB.
| |
Primary Examiner: Mengistu; Amare
Attorney, Agent or Firm: Iandiorio & Teska
Parent Case Text
This is a continuation of application Ser. No. 08/031,614, filed Mar. 15,
1993, now abandoned.
Claims
What is claimed is:
1. A system for sensing the position of a stylus proximate a display device
employing a matrix of display electrodes which generate display electrode
signals, wherein the position sensing and display functions are performed
simultaneously, comprising:
means for generating in the stylus positioning signals;
means for coupling said positioning signals to the display electrodes and
for superimposing said positioning signals onto the display electrode
signals;
means for sensing said positioning signals from the display electrodes; and
means, responsive to said means for sensing, for resolving the position of
the stylus in relation to the display electrodes.
2. The stylus position-sensing system of claim 1 in which said means for
coupling from stylus to display electrodes includes means for magnetically
transferring said positioning signals to the selected display electrodes.
3. The stylus position-sensing system of claim 2 in which said stylus has
no electrical connection to the display device.
4. The stylus position-sensing system of claim 1 in which the display
device is an LCD.
Description
FIELD OF INVENTION
This invention relates to a display-integrated stylus detection system that
uses the display electrodes as part of the system.
BACKGROUND
The task of locating a stylus with respect to a display device has been
solved by a number of methods. CRT monitors have been used with light pens
and touch screens for this purpose. Stylus position detection on flat
panel displays has been done with touch screen technology and electronic
digitizer technology. Some specific implementations are described below.
Light Pens
A light pen senses the change in light from the CRT phosphor as the
electron beam passes within the light pen's field of view. The position of
the pen relative to the display is calculated by timing the pen's light
detection signal versus the known time/position relationship of the CRT
scanning system. Light pens have the advantage that they do not require an
overlay in front of the display.
Although light pens are useful for CRT monitors, they are not suitable for
displays which do not emit light, such as LCD's, or for displays which are
not refreshed by a regular, repetitive scanning sequence, such as plasma
displays and LCD's. In addition, the accuracy of a light pen is limited
and it is dependent on variables such as display brightness and scan
timing.
Touch Screen Technology
Touch screen technology has been used to implement the digitizer function
in conjunction with displays. Touch screens provide the advantage of
transparency, such that they may be used as an overlay in front of a
display.
Touch screens use a variety of methods to detect the position of a stylus
or a person's finger relative to a display. Methods of implementing touch
screens include transparent conductive coatings on glass, arrays of light
beams, and surface acoustic waves. The devices using conductive coatings
on glass have been applied to writing stylus applications in addition to
finger touch. All of these methods require a sensing apparatus which is
independent of the display.
W. Pepper, Jr's U.S. Pat. Nos. 4,071,691; 4,129,747; and 4,198,539 describe
position sensing devices which have been implemented in practice as touch
screens consisting of a transparent resistive surface on a glass
substrate. This device is sufficiently transparent that it may be placed
in front of a display device. In this application, coordinates derived
from the touch screen may be mapped to the coordinates of the display. The
Grid Pad product introduced in 1989 by Grid, Inc. uses a resistive sheet
overlay device based on W. Pepper, Jr's patents. The Grid device uses a
stylus for pointing and hand drawn graphic input.
U.S. Pat. Nos. 4,220,815 and 4,220,815 by W. A. Gibson, et.al describe
another touch screen implementation using a conductive coating on glass
with a plastic overlay. The methods used in these patents were also
applied to a stylus based writing input device in U.S. Pat. No. 3,911,215
by G. S. Hurst and W. C. Colwell, Jr.
All of these devices have the disadvantage that they require an overlay of
glass and/or metal films over a display device, which adversely affects
display optics. Also, the digitizer function is not inherently aligned
with the display device with which it is used. Accordingly, alignment must
be accomplished mechanically, or through computation.
Magnetic & Electrostatic Digitizers
Magnetic and electrostatic digitizer technology has been applied to stylus
position detection, and these have been used in combination with flat
panel displays to locate the stylus relative to a display. Sony introduced
the PalmTop PTS-500 product in 1990 for sale in Japan. This uses a
separate digitizer overlaid in front of an LCD display to detect the
position of a stylus. The digitizer is a magnetic or electrostatic type
built on a glass substrate with nearly transparent electrodes.
This has the disadvantage that the digitizer glass and electrodes cause
optical interference with the display. Also, the digitizer coordinate
system is not inherently aligned with the display.
A display/digitizer configuration has been proposed and tested with an LCD
display placed physically in front of an electromagnetic digitizer. In
this case, the electromagnetic fields of the digitizer permeate the LCD
and its backlighting system to locate the position of a stylus in front of
the LCD. This system has the advantage of eliminating the optical
interference of a digitizer overlay in front of the display. It also has
significant technical and functional disadvantages. For example, the
accuracy of an electromagnetic digitizer decreases as the distance between
the digitizer surface and the stylus increases. Placement of metals and
other conductive objects (e.g. the LCD display) between the stylus and the
digitizer surface will decrease accuracy of the digitizer. The large
distance between the stylus and the digitizer surface will cause parallax
errors in position measurements Also, noise emitted from the display will
cause errors in the digitizer system.
Digitizers & Detectors Integrated with a Display
U.S. Pat. No. 4,839,634 by E. S. More and U.S. Pat. No. 4,841,290 by M.
Nakano et. al. have advantages over the other prior art described above.
In both of these patents, the input device integrates a flat panel display
with a digitizer and stylus, eliminating two major disadvantages: the
digitizer/display alignment problem and the optical interference from an
overlay. Both use a modified flat panel display for this purpose.
The major benefit to the two approaches is that they use the X/Y electrode
pattern of the display to perform position sensing as well as data
display. A major problem with both approaches is that they alternate use
of the electrodes between the display and position-sense functions.
Time-sharing of display drive signals in this way will result in several
problems:
Contrast and field of view of passive matrix LCD's are dependent on the
amount of time available for driving each pixel. Reducing this time by
time-sharing with another function will reduce display quality.
The required data rate for text input is about 100 to 200 samples per
second. The More patent stresses the need for fast sampling, but the
example given is for 30 samples per second. This sample rate is
insufficient for the task, and it will be limited by the disclosed
display/position signal alternating approach.
Alternating the electrode drive from screen refresh to position sensing
necessitates interrupting the physical display drive signals and gating or
multiplexing them. This means a display cannot be retrofitted with this
technology; it must be built in. The display driver electronics of many
displays are physically integrated with the display such that addition of
multiplexers is a significant mechanical problem as well. This is
specially true of LCD's.
The Nakano patent is also limited to transmitting magnetically from an X/Y
matrix display and receiving in a stylus. Neither More nor Nakano
addresses the issue of edge effects at the periphery of their electric or
magnetic fields.
U.S. Pat. No. 4,363,029 describes a means of detecting a finger touch on an
LCD display. The method involves sensing the change in capacitance of an
LCD element due to proximity of a person's finger. The change is detected
relative to a reference capacitance element in the device. This detects
the presence of a finger touch in proximity with a discrete display
element only; it does not detect position. This method is suitable for
detection of touch on a small LCD display, but it cannot be used to detect
position on a large LCD with hundreds or thousands of display elements.
Also, this method requires a reference element for each display element
which does touch detection.
U.S. Pat. No. 4,893,115 describes an integrated display & touch screen
device. This approach has the advantage that it is self-aligning to the
display. It has the disadvantage that it needs an overlay in front of the
display to shunt the display signals in response to a touch.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide a display-integrated
stylus detection system in which the optical qualities of the display are
not hindered by the digitization device.
It is a further object of this invention to provide such a system in which
the digitized coordinates are inherently aligned with the displayed
images.
It is a further object of this invention to provide such a system in which
the display electrodes are used as part of the digitizer.
It is a further object of this invention to provide such a system in which
the digitizer is integral with the display.
It is a further object of this invention to provide such a system in which
optical parallax between the digitizer and the display is minimized.
It is a further object of this invention to provide such a system in which
the digitizer function may be added to an existing display.
It is a further object of this invention to provide such a system having a
relatively simple and inexpensive digitizer function.
It is a further object of this invention to provide such a system which
allows digitizer data rates which are sufficient to measure handwritten
graphical input.
It is a further object of this invention to provide such a system in which
an untethered digitizer stylus may be employed.
It is a further object of this invention to provide such a system in which
the display output quality is not affected by the digitization signals.
It is a further object of this invention to provide such a system in which
digitizer signals may be transmitted from a stylus and received by display
electrodes.
It is a further object of this invention to provide such a system in which
edge effect accuracy problems are decreased for the stylus-transmitting
embodiment.
This invention results from the realization that a truly effective
digitization system may be accomplished with an existing display having
display electrodes by superimposing positioning signals on the display
electrodes and sensing those signals with a stylus, or transmitting from
the stylus and sensing their effect on the display electrode drive
signals, to accomplish an inherently aligned retrofittable digitization
system that has no effect on the optical qualities of the display itself.
This invention features a system for sensing the position of a stylus
proximate a display device employing a matrix of display electrodes. The
system includes means for generating stylus-positioning signals from
either the stylus or the display electrodes, or alternating between the
two, and means for sensing an effect of those signals from the other of
the stylus and display electrodes in response to the sensed effect. There
are means for resolving the position of the stylus in relation to the
display electrodes. The positioning signals may be coupled to the display
electrodes directly, capacitively or magnetically. The position of the
stylus may be resolved by determining the relative strengths of the sensed
signals, or the relative phase of the sensed signals. The sensing may be
accomplished by detecting electrostatically or electromagnetically the
positioning signals.
The positioning signals may be sequentially coupled to different display
electrodes, and in that case the stylus position may be resolved based on
timing of the sequential coupling. Preferably, the positioning signals are
AC signals that may be superimposed on the display matrix drive signals
without interrupting the display and without the need for multiplexing the
display drive signals. As a result, the invention has no effect on the
display quality. The signals may be superimposed with amplifiers for
driving positioning currents in the display electrodes. An AC
electromagnetic signal may be selectively generated in the stylus and the
system may further include means for selectively sensing the signals
induced by the electromagnetic signal and selected display electrodes. In
that case, the means for resolving may be selectively responsive to the
means for sensing the induced signals for determining the stylus position
from the induced signals.
In one embodiment, the stylus has no electrical connection to the display
device. The signals may be coupled from the stylus to the display
electrodes through capacitive or magnetic transference. Further, the
position signals may be sensed from the display electrodes through
capacitive or magnetic coupling. This may be accomplished with a
transformer winding proximate one or more display electrodes. The display
device may be an LCD.
DISCLOSURE OF PREFERRED EMBODIMENTS
Other objects, features and advantages will occur to those skilled in the
art from the following description of a preferred embodiment and the
accompanying drawings, in which:
FIG. 1 is a block diagram of a display-integrated stylus detection system
according to this invention;
FIG. 2 is a more detailed schematic diagram of one way of implementing the
system of FIG. 1 in which the display matrix can be used to either send or
receive digitization signals;
FIG. 3 is a schematic diagram of another implementation of the system of
FIG. 1 in which the display matrix can also be used for either sending or
receiving the digitization signals;
FIG. 4 is a schematic diagram of yet another manner of implementing the
system of FIG. 1;
FIG. 5A is a schematic diagram of yet another means of implementing the
system of FIG. 1 in which the display matrix is used to transmit the
digitization signal;
FIG. 5B is aschematic diagram of a system similar to that of FIG. 5A, but
which uses the display electrode matrix for digitization signal reception;
FIG. 6 is a schematic diagram of a signal-receiving or generating stylus
tip for use in the system of this invention.
This invention includes a means of using the electrodes of a display device
as part of a position sensing circuit. The position sensing signals are
mixed with the display refresh signals on the display electrodes; i.e. the
electrical positioning signals are superimposed on the display signals in
such a way that they do not interfere with the display function.
There is shown in FIG. 1 display-integrated stylus detection system 10
according to this invention. System 10 is integrated with matrix display
12 comprising X and Y matrixes of crossed wires connected to X display
driver 16 and Y display driver 14, for example a commonly-known LCD
device. The system of this invention is integrated into the LCD display
device using X position signal driver 18 and Y position signal driver 20
in conjunction with stylus 22 and position sensing driver circuit 26. X
position signal transmitter and receiver 18 superimposes digitization
signals on the portion of the matrix driven by X display driver 16 as is
described below. Similarly, Y position signal driver 20 superimposes
digitization signals on the display drive signals generated by Y display
driver 14. Stylus 22 then senses these digitization signals and reports
the sensing to circuit 26 which, in conjunction with timing or frequency
signals from drivers 18 and 20, determines the position of stylus 22 in
relation to display matrix 12.
In an alterative operating mode, the digitization signals may be
transmitted from stylus 22 and received by position signal receivers in
the place of 18 and 20. Another alternative operating mode is to include
both transmission and reception functions in circuits 18 and 20 and stylus
22 so that the transmission and reception can be alternated as desired
between the display device and the stylus.
FIGS. 2, 3 and 4 show four electrodes of a liquid crystal display (LCD)
12a, 12b and 12c, respectively, in the X (horizontal) direction, and 4
electrodes in the Y direction.
System 10a, FIG. 2, operates with Y position signal driver 20a and X
position signal driver 18a which use amplifiers that are capacitively
coupled to every other electrode of electrode matrix 12a; this connection
scheme is schematically depicted by virtual capacitors 50, 51, and 60, 61,
respectively. The LCD display drive amplifiers 30 through 33 and 40
through 43 already present in the display device act as the terminators or
current sinks for the position signals. System 10a may also be used in an
embodiment in which a position signal is transmitted from a stylus
proximate the display surface and the display electrodes are used to
receive the signal, in which case the X and Y position amplifiers in
circuits 18a and 20a, respectively, are used for receiving rather than
transmitting signals.
FIGS. 3, 4, 5A and 5B disclose different means of conveying current through
the electrodes of the display. In the transformer coupled embodiment 10b
of FIG. 3, transformers 82 and 92 are used to pass current between a
position amplifier and a display electrode. In practice there would be one
amplifier and transformer for each display electrode used for sensing.
This approach is preferred where the display drivers have insufficient
current drive to support the position sense current. This type of
differential signal driver approach can also be achieved with methods
other than a transformer signal source. For example, differential
transconductance amplifiers 102 and 104, FIG. 4, may be used in place of
transformer windings 92 and 82, FIG. 3. As with the embodiment of FIG. 2,
the embodiment of FIG. 3 may be used in a system in which the stylus sends
the signal which is coupled to the matrix conductors and then sensed
through the transformer windings.
The embodiment of FIG. 4 uses transconductance amplifiers such as
amplifiers 102 and 104 in place of the transformer windings of FIG. 3.
This embodiment can also be used for stylus-sensing embodiments. Yet
another alternative for transmitting position signals from the matrix is
shown in FIG. 5A, in which signal generators 110 and 116 in conjunction
with power supplies 112 and 114, respectively, are used to generate the AC
signal which is superimposed on the matrix drive signal at drive
amplifiers 14d and 16d. For a stylus-transmitting embodiment of this type
of circuit, FIG. 5B, signal measuring amplifiers 124 and 134 are used in
conjunction with resistors 122 and 132 to measure the received signal
which is superimposed on the drive signal wave forms as a result of
coupling from the stylus which transmits stylus position signals generated
in conjunction with stylus position signal transmission circuit 26a to the
matrix conductors. As before, the circuit for only one display matrix is
shown. In practice, there would be one such transmit and/or receive
circuit for each matrix electrode employed in stylus position sensing.
The following relates to the embodiments of each of FIGS. 2, 3, 4 and 5A,
unless otherwise noted.
Each electrode of the display is driven by a display driver which imposes a
multi-level voltage signal with a certain waveshape as required to
activate pixels at the electrode intersections. This is known in the art
of such matrix displays. Display drivers are generally voltage output
devices which have low output impedance when they are driving the display.
The X/Y Position circuits of this invention may be added to the display
circuit as follows:
1. AC Positioning signals are connected to certain display electrodes by
either capacitive or magnetic coupling or by direct connection.
2. These Positioning signals are of high enough frequency and small enough
magnitude that they do not interfere with the voltages which drive the
display.
3. The AC positioning signals induce currents which flow through the
display electrodes, (across the visible portion of the display) and into
the Display driver outputs (as in FIG. 2), or back into the position
circuit (as in FIGS. 3 and 4).
4. The magnetic fields produced by the AC positioning signals are detected
by a detecting circuit. Currents are induced sequentially in the
electrodes (or they use different frequencies or waveforms), so the signal
received by the detecting circuit from each electrode is differentiable
from the others. Also, it is possible to interpolate between the signals
from adjacent current carrying electrodes, to achieve resolution finer
than the distance between current carrying electrodes. It is also possible
to transmit from the stylus and receive at the electrodes, or to
alternately transmit from, then receive to the electrodes.
5. A typical LCD display has electrodes on about 0.015" centers. It is not
necessary to drive all display electrodes for position sensing. Typical
electromagnetic digitizers require drive electrodes at 0.2" distance or
more.
6. Coupling of position signals into the display electrodes may be done by
making direct electrical contact with the electrodes, or capacitive
coupling may be made by placing the positioning signals in close proximity
with the appropriate display electrodes. In a similar manner, magnetic
coupling of the positioning signals may be used to convey the signals to
the display electrodes.
7. These methods may be applied to many types of displays, including
passive or active LCD's, and to matrix displays other than LCD's, (for
example, to plasma or electroluminescent displays).
8. These methods may be used to integrate position sensing into a display
at the time of manufacture, or to retrofit the position sense circuits
after manufacture of the display.
The preferred embodiments described above do not require specific position
signal connections to the display driver amplifiers. It may be preferable
in some cases to use the display driver circuits to transmit both the
display signals and the superimposed position signals to the display
electrodes. This may be done by one of three methods. First, the display
driver circuit can be modified to internally mix the display and position
signals. Alternatively, an additional mixing circuit can be added to the
output of the display driver. Finally, the display driver signal can be
modulated by external means. FIG. 5A shows a circuit configuration 10d
where the power supply input to standard LCD display drivers is modulated
with position signals. Superimposing position signals onto the driver
power supply will cause the driver to mix the display and position data so
its output is a combination of both signals.
The following are applicable to any of these three methods of implementing
driver-mixed positioning signals.
1. AC Positioning signals are connected to certain display electrodes
through the display driver outputs.
2. The Positioning signals are of high enough frequency and small enough
magnitude that they do not interfere with the voltages which drive the
display.
3. The AC positioning signals induce modulated voltages on the display
electrodes. These modulation signals may be detected either
electrostatically or electromagnetically by a detector circuit on or above
the display surface. This position information is then used to determine
the position of said detector circuit.
4. In the case of electrostatic detection, the electric fields produced by
the AC positioning signals are detected by a detector circuit. Voltages
are induced sequentially in the electrodes (or they use different
frequencies), so the signals received by the detector circuit from each
electrode is differentiable from the others. Also, it is possible to
interpolate between the signals from adjacent current carrying electrodes,
to achieve fine resolution. It is also possible to transmit from the
stylus and receive at the electrodes, or to alternately transmit from,
then receive to the electrodes.
5. A typical LCD display has electrodes on about 0.015" centers. It is not
necessary to drive all of these electrodes for position sensing.
6. Electromagnetic coupling of position signals will require current
flowing through the display electrodes. For this, a terminator circuit is
required at the end of each electrode opposite from the driver amplifier.
Terminator circuits may be connected by making direct electrical contact
with the display, or capacitive coupling may be made by placing the
terminator circuits in close proximity with the appropriate display
electrodes. In a similar manner, magnetic coupling may be used to connect
the terminator circuits to the display electrodes.
7. These methods may be applied to passive or active LCD's, and to matrix
displays other than LCD's, (for example, to plasma or electroluminescent
displays).
An alternative embodiment would be to transmit position signals from the
stylus.
These signals are coupled to the display electrodes, overlaid on the
display signals, and then are detected as follows:
Refer to FIGS. 2, 3 and 5A; each of the figures show four electrodes of a
liquid crystal display (LCD) in the X (horizontal) direction, and 4
electrodes in the Y direction. A position signal is transmitted from a
stylus which is proximate to the display surface. An embodiment of such a
stylus 22a is shown in FIG. 6. Stylus 22a includes wire loop 24 positioned
in the stylus tip to transmit or pick up signals for an electromagnetic
sensing system. Twisted wire pair 25 passes through shield 27 as is known
in the art.
Circuit 10b of FIG. 3 differs from circuit 10a of FIG. 2 in its method of
detecting position current from the electrodes of the display; circuit 10a
picks up the position signal from a position amplifier which is
capacitively coupled to certain of the display electrodes. Circuit 10b,
FIG. 3, detects current induced into the display electrodes from the
stylus by use of a transformer winding connected to the display electrode.
This approach is preferred where the display drivers have insufficient
current drive to support the position sense currents. This differential
signal detector approach can also be achieved with methods other than a
transformer signal source. For example, a differential amplifier with high
common mode impedance and low differential impedance may be used in place
of the transformer windings.
All comments below refer to the embodiments of FIGS. 2, 3, and 5B for
matrix receiving embodiments, unless otherwise noted.
Each electrode is driven by a display driver which imposes a multi-level
voltage signal with certain waveshape as required to activate pixels at
the electrode intersections. Display drivers are generally voltage output
devices which have low output impedance when they are driving the display.
X/Y Position circuits are added to the display circuits as follows:
1. AC Position signal detector circuits are connected to certain display
electrodes by either capacitive or magnetic coupling or by direct
connection.
2. Positioning signals are transmitted from a stylus proximate to the
display surface. These signals are of high enough frequency and small
enough magnitude that they do not interfere with the voltages which drive
the display.
3. The AC positioning signals coupled from the stylus induce currents which
flow through the display electrodes, (across the visible portion of the
display) and into the Display driver outputs (as in FIGS. 2 and 5B), or
back into the position circuit (as in FIG. 3).
4. The currents produced by the AC positioning signals are detected by a
detecting circuit. Induced currents have different phase and magnitude in
different electrodes such that the stylus position relative to them may be
determined. Also, it is possible to interpolate between the signals from
adjacent current carrying electrodes, to achieve resolution finer than the
distance between current carrying electrodes.
5. A typical LCD display has electrodes on about 0.015" centers. It is not
necessary to receive from all display electrodes for position sensing.
Typical electromagnetic digitizers require drive electrodes at 0.2"
distance or more.
6. Coupling of position signal detector circuits to the display electrodes
may be done by malting direct electrical contact with the electrodes, or
capacitive coupling may be made by placing the positioning signal detector
circuit in close proximity with the appropriate display electrodes. In a
similar manner, magnetic coupling of the positioning signals may be used
to convey the signals to the detector circuits.
7. These methods may be applied to many types of display, including passive
or active LCD's, and to matrix displays other than LCD's, (for example, to
plasma or electroluminescent displays).
8. These methods may be used to integrate position sensing into a display
at the time of manufacture, or to retrofit the position sense circuits
after manufacture of the display.
Although specific features of the invention are shown in some drawings and
not others, this is for convenience only as some feature may be combined
with any or all of the other features in accordance with the invention.
Other embodiments will occur to those skilled in the art and are within the
following claims:
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